The present invention is directed to an expansion dowel assembly with expansion members displaceable radially outwardly under spring tension, a support bearing including load engagement surfaces located, in the assembly, ahead of the expansion member in the insertion direction of the dowel into a receiving material, and a detachable tension member clamps the expansion members in a radially inward position so that the assembly can be inserted into a bore hole.
Expansion dowels which penetrate into a bore hole in a receiving material axially abut at shoulders within the bore hole in a positive locking manner are used increasingly in crack-prone regions for fastening objects to the receiving material, such as concrete. The shoulders can be in the form of a widened undercut in the bore hole or of the inner side of the receiving material penetrated by the bore hole.
Such an expansion dowel is disclosed in U.S. Pat. No. 3,241,420 and includes a support bearing for two-arm expansion members pivoted so that they can be displaced outwardly diametrically opposite one another under spring tension. The support beings also has load engagement means in the form of an internal thread into which a bolt or fastening member can be screwed for securing a load to the expansion down. A tension member retains the expansion member under an elastic force in an inwardly shifted position when the dowel is inserted into a bore hole, thereby preventing the development of frictional forces between the expansion members and the surface of the bore hole. After the free ends of the expansion members have reached the shoulder formed, for instance, by the inner side of the receiving material, the expansion members are released by an auxiliary tool through the displacement of the support bearing.
The outward displacement of the expansion member is limited by abutment means. Because of the abutment means, the known expansion dowel has one single defined expansion position where it abuts rigidly against the receiving material in the direction opposite to the insertion direction into the material. Accordingly, problems develop under dynamic loading and there is no possibility to compensate for relaxation of the receiving material. Moreover, the contacting abutment of the free ends of the expansion member against the receiving material leads to high specific compression stresses in the expansion member and in the receiving material.